In some electronic apparatus, e.g. digital answering machine, stringent requirement for a non-defective memory device used to store the voice data, either the answering information or the incoming information, is not necessary. Therefore, the Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), EEPROM or Flash memory, having defective cells at unknown locations and being not acceptable in other applications, is used in some audio applications and is known as Audio Grade RAM (ARAM).
It is well known that a data compression/decompression technique is generally employed in most audio data processing, which involves mass amount of data, to handle the data more efficiently. However, when ARAM is employed together with the data compression/decompression technique in the digital audio apparatus, the voice data obtained from the data decompression procedure may be over-distorted such that the output may not well identified by the human beings. Accordingly, an algorithm is required to assure the original data are stored within the non-defective cells of an ARAM.
One conventional approach is to record the address of the defective cells during the power-on period of the system into the a predetermined range of cells of the memory. And all access operations avoid the recorded addresses by the information stored in this predetermined range. However, this approach requires non-defective cells at the predetermined range of locations. This approach indirectly places a requirement of a sorting procedure on the ARAMs to assure all ARAMs used are non-defective at the predetermined range of locations.
Another conventional approach uses the concept of the FORMAT command in Disk Operating System (DOS) supplied by Microsoft Co.. This approach first partitions the memory into a plurality of good sectors and the data are stored in several good sectors. Each sector is linked to next associated sector by the linking address stored at the end of each sector. The defective cells are therefore circumvented.
Still another approach uses error correction algorithm and a corresponding check bit to correct any incorrect bit obtained from the defective memory. However, this approach requires associated hardware circuit and the cost thereof are elevated.
Therefore, it is the object of the invention to provide a less complicated and less expensive way to use a memory device having defective memory cells.